Field of the Invention
The present invention relates to a data communication device, an information visualizing system and a data communicating program and is suitably used in an information visualizing system for analyzing data collected in a server from a plurality of portable terminals and visualizing a result of the analysis to provide the visualized result to a terminal of a display request source and to display the visualized result thereon, for example.
Description of the Related Art
Conventionally, there is provided an information visualizing system for analyzing many data collected in a server from a large number of portable terminals and visualizing a result of the analysis so as to be easily understood visually, providing the visualized result to a client terminal and displaying the visualized result thereon. As an example of the information visualizing system, there is known a geographic information system (GIS) for visualizing a result of analysis and displaying the visualized result on a map (for example, see Patent Documents 1 and 2).
Referring to the map displaying system described in the Patent Document 1, a server receives and stores a current place from a portable terminal carried by a pedestrian or the like or an on-vehicle terminal through internet. Then, there are generated map image data for displaying a map image where a user mark representing an area including a current place of a corresponding terminal and indicating a current place of a pedestrian in the area or a vehicle mark indicative of a current place of a vehicle is drawn, and the map image data are transmitted to a corresponding terminal. On the other hand, a terminal receiving the map image data displays a map image through a web browser based on the map image data.
In the viewing possibility information providing system described in the Patent Document 2, a portable apparatus periodically detects a current position and decides a viewing possibility of a television broadcasting signal of at least one broadcasting station in that position. A result of the decision is accumulated in a server through a communication network. Based on the accumulated data, indices representing the results of the decision are superimposed and displayed in respective positions on a map around the current position.
Referring to the system for collecting a large number of data from a large number of portable terminals and analyzing them through a server and displaying marks representing current positions of the respective portable terminals on map images one by one in superimposition as described in the Patent Documents 1 and 2, map image data to be generated by the server and transmitted to a client terminal have an enormous data volume so that a communication load is extremely large. For this reason, there is a problem in that a long time is taken for communication and a turnaround time for displaying a map image on the client terminal is thus prolonged. In particular, it is hard to update, in real time, information which might be changed moment by moment, for example, a current position, a result of decision of a viewing possibility or the like and to display them on the client terminal.
There is known the technology for transmitting only difference data having a change generated, thereby reducing a communication load (see Patent Documents 3 to 5, for example). In the information management system described in the Patent Document 3, a mobile station device (a vehicle server) is provided in a mobile station (a war vessel) and serves to record data to be collected in the mobile station and to transmit difference information indicative of a changed part of data to a fixed station in a predetermined cycle.
Referring to the data transfer method descried in the Patent Document 4, when packetizing monitored information in a monitored device and transmitting the packetized information to a monitoring device through a transmission path, it is possible to efficiently use a transmission path having a limited capacity by extracting only a changed part of the packetized information to transmit a difference packet with a transmission packet data volume reduced.
Referring to the data difference distributing method of the compressed described in the Patent Document 5, it is possible to reduce a data size to be distributed, thereby shortening a time required for distribution by distributing a difference between old data and new data.    [Patent Document 1] Japanese Laid-Open Patent Publication No. 2013-45238    [Patent Document 2] Japanese Laid-Open Patent Publication No. 2006-115257    [Patent Document 3] Japanese Laid-Open Patent Publication No. 2005-258582    [Patent Document 4] Japanese Laid-Open Patent Publication No. 1993-191454    [Patent Document 5] Japanese Laid-Open Patent Publication No. 2011-60039